"Martian Child" commits every crime of sentimentality that its director, Menno Meyjes, was wrongly accused of in his career-making screenplay for "The Color Purple."

David Gerrold's semi-autobiographical novelette about a sci-fi author who adopts a strange, difficult little boy was easy enough to sap up. Gerrold's prose is plainspoken and heartfelt, leaving room for a filmmaker to apply filters of ironic cynicism or, conversely, schmaltz. Meyjes goes for the schmaltz. His screenwriters, Seth Bass and Jonathan Tolins, seem to have had something tougher and subtler in mind. With a screenplay tailored for John Cusack in the role of adoptive father, the film buries Cusack's tough-minded charisma under heaps of sugar.

The sugar starts pouring early on, as the titular child, Dennis (Bobby Coleman), who believes he's from the planet Mars, steals the heart of grieving widower David (Cusack). The boy walks around in a cardboard box, peering warily out of a slit on its side. David lures him out of the box by playing "catch" with a ball. Aaron Zigman's wonderstruck musical score wants this to be a magic moment, but Meyjes renders this mysterious little "creature" making contact with a human through child's play less reminiscent of "E.T." than its bizarro imitator, "Mac and Me."

David seeks to adopt the boy, thinking that his Martian fantasies are just a way of coping with loss and loneliness. As a professional fantasist, he can relate. But when the kid's beliefs don't go away during an adoption trial period, David starts to wonder if there's some truth to the boy's claim. David's natural child-like imagination allows him to take a tour of Dennis' alien(ated) world.

"Martian Child" is a decades-old labor of love for producer David Kirschner, but there is something disingenuous and calculating about the work of his director and composer. While Dennis seems to believe so purely in his Martian-ness that he doesn't show much concern for what people think, Meyjes and Zigman work overtime to assure the audience that he's a good boy deep down, no worries -- and ain't he cute?

Coleman has the eerie authenticity and adult intelligence of child stars like Haley Joel Osment and Dakota Fanning, but Meyjes seems as afraid of the trauma and desolation in Dennis' little eyes as the hapless caseworkers and adoption agents who don't know what to do with him.

Cusack does his best to do what his character is advised to do for Dennis, keep both feet on the ground. His realism brings some gravity to the film's midsection, where David and Dennis are left alone to figure out how to live together. By the time an adoption offical (Richard Schiff) threatens to end their relationship just when it starts making progress, Cusack's desperate profession of love for the boy is an emotional sucker punch equal to the heart-tugging confessions in the home stretch of Meyjes' "The Color Purple" script. For a few intriguing moments, Meyjes stops trying to sell us on the wonder of it all and just records the chemistry between Cusack and Coleman.

Otherwise, "Martian Child" lazily presents itself as a foregone series of meet-cutes and epiphanies already cued up for an inspiring Oscar Night montage. In a film choked with product placements, the consumer item it hawks most aggressively is itself.